Packages for electronic components includes a number of electrical circuit components such as transistors, diodes, capacitors, inductors and resistors. In many cases several components are collected on one integrated circuit.
Integrated circuit chips need encapsulation for a variety of reasons. The integrated circuits require mechanical support, protection against the environment, a supply of power, signal terminals and the removal of heat.
Hence the major functions of the package are circuit support and protection, atmosphere control, power distribution, signal distribution and heat conduction.
As a rule more than one packaging level is required to satisfy these conditions. The chip package constitutes the first level of packaging. At least one more level is usually employed because the number of functions needed may exceed those available on a single first level package.
The emergence of Very Large Scale Integration (VLSI) chips simplified circuit design but also increased the complexity of the majority of package designs. Many electric functions could be achieved on a few VLSI chips, which were mounted in packages. The chip packages were mounted on a board. If needed, some discrete components were mounted on such a board together with the VLSI chip packages. Boards, however, often became very complex because a high number of chip terminals were concentrated on a small area.
An alternative to boards emerged when higher wiring densities were achieved with hybrid technology and ceramic packages such as chip carriers, flat packs, pin-grid arrays and more complex packages which were capable of supporting from one chip to more than a hundred chips per package. It was possible to put several VLSI chips and discrete components on the same substrate, and connect them with each other via multilayer conductors on the substrate. It was still, however, necessary to interconnect many VLSI-chips with moderate dimensions and a limited number of pads within one or a few hybrid circuits in order to achieve high performance signal processing.
Connections between chip and package are commonly performed by wire bonding, soldering, or Tape Automated Bonding. Wire bonding is the most common chip-bonding technology, but it has limitations. One of the constraints is that thermal dissipation is limited mainly to the back of the chip.
In the latest edition of "Microelectronics Packaging Handbook" by Rao R. Tummala and Eugene J. Rymaszewski, 1989, the maximum number of connections per chip expected to be feasible with TAB technology is rated at 600 connections/chip. Regarding wire bonding the prediction was about 260 connections/chip. Manufacturing technology in 1988 allowed for 257 connections/chip by wire bond and 320 connections/chip by TAB.
As will be shown later in this specification a package is disclosed which exceeds the above expectations.
Packaging today can be divided into two main types, the ceramic package and the plastic package. Ceramic packages generally have better performance, while plastic packages usually have the advantage of being cheaper.